1. Field of the Invention
This invention generally relates to a communication control system, and, in particular, to such a communication control system including a telephone unit and a data communication apparatus which are switchingly used for communication via a common transmission line connected to the communication control system.
2. Description of the Prior Art
In the recent information-oriented society, facsimile machines are widely used and many personal computers having a communication function are available. In such data communication apparatuses as facsimile machines and personal computers having a data communication function, data is typically transmitted using a telephone network. If the frequency of use of such a data communication apparatus is not so great, the telephone transmission line which has already been installed is often used also for such a data communication apparatus, and for this purpose a switching device is provided for switching a connection to the telephone transmission line between a telephone unit and a data communication apparatus, such as a facsimile machine. In such a case, the telephone unit is typically placed on a most convenient place, such as on a desk or on a wall; on the other hand, the data communication apparatus is located at such a place where an operator can use the apparatus most conveniently and where there is enough space for installation of such an apparatus, such as in a room or office. As a result, it is often the case that the telephone unit and the data communication apparatus are located at remote places, though they are connected to a common switching device since they both use the same telephone transmission line for communication. Since both of the telephone unit and the data communication apparatus are connected to the common switching device which in turn is connected to a single transmission line connected to a telephone network, they must be switchingly connected to the transmission line through the switching device.
Recent data communication apparatuses are often so structured that they can accept a request for conversation sent from another data communication apparatus at a remote place even in the process of data communication and upon completion of data communication a buzzer mounted in the data communication apparatus is activated to give an audio warning to the operator. Thus, the operator comes to know that a request for conversation has been received by this audio warning and then picks up the handset of the telephone unit to initiate telephone conversation with a caller.
In such a prior art structure, however, since the buzzer is mounted in the data communication apparatus, the activation of the buzzer may not be noticed by the operator This is likely because the data communication apparatus is often located in such a place where people do not stay long; on the other hand, the telephone unit is usually located at a place where ringing can be heard by most of the people concerned. Thus, in accordance with the above-described prior art structure, even if there has been a request for conversation, there is a chance that such a request be neglected.